It's useful, but you should keep it on the simple side, IMHO. For example here is a small part of my daytrade scalper program. Something like this is all you really need:
<P>
(1) <IMG BORDER=0 ALIGN=TOP ALT="" SRC="http://ej.iop.org/images/0305-4470/30/6/004/Full/img66.gif">, iff <i>V</i>(<i>x</i>) is an arbitrary
differentiable function;
<P>
(2) <IMG BORDER=0 ALIGN=TOP ALT="" SRC="http://ej.iop.org/images/0305-4470/30/6/004/Full/img67.gif">, iff <IMG BORDER=0 ALIGN=TOP ALT="" SRC="http://ej.iop.org/images/0305-4470/30/6/004/Full/img68.gif">;
<P>
(3) <IMG BORDER=0 ALIGN=TOP ALT="" SRC="http://ej.iop.org/images/0305-4470/30/6/004/Full/img69.gif">, iff
<IMG BORDER=0 ALIGN=TOP ALT="" SRC="http://ej.iop.org/images/0305-4470/30/6/004/Full/img70.gif"> the following equalities are true:
<P><IMG BORDER=0 ALIGN=TOP ALT="" SRC="http://ej.iop.org/images/0305-4470/30/6/004/Full/img71.gif"><P>
<P>
(4) <IMG BORDER=0 ALIGN=TOP ALT="" SRC="http://ej.iop.org/images/0305-4470/30/6/004/Full/img72.gif">, iff <IMG BORDER=0 ALIGN=TOP ALT="" SRC="http://ej.iop.org/images/0305-4470/30/6/004/Full/img73.gif">,
<IMG BORDER=0 ALIGN=TOP ALT="" SRC="http://ej.iop.org/images/0305-4470/30/6/004/Full/img74.gif"> are constants and (9) are true. <IMG BORDER=0 ALIGN=TOP ALT="" SRC="http://ej.iop.org/images/0305-4470/30/6/004/Full/img75.gif">
are the binomial coefficients.
<P>
The operators in theorem 3 have the following representation:
<P><IMG BORDER=0 ALIGN=TOP ALT="" SRC="http://ej.iop.org/images/0305-4470/30/6/004/Full/img76.gif"><P>
<i>I</i> is the unit operator.
<P>
<i> Consequence</i>. The 2<i>n</i>th-order PDE
<P><IMG BORDER=0 ALIGN=TOP ALT="" SRC="http://ej.iop.org/images/0305-4470/30/6/004/Full/img77.gif"><P>
is invariant under the following algebras:
<P>
(1) <IMG BORDER=0 ALIGN=TOP ALT="" SRC="http://ej.iop.org/images/0305-4470/30/6/004/Full/img78.gif">, iff <i>V</i>(<i>x</i>) is an arbitrary
differentiable function;
<P>
(2) <IMG BORDER=0 ALIGN=TOP ALT="" SRC="http://ej.iop.org/images/0305-4470/30/6/004/Full/img79.gif">, iff <IMG BORDER=0 ALIGN=TOP ALT="" SRC="http://ej.iop.org/images/0305-4470/30/6/004/Full/img80.gif">;
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(3) <IMG BORDER=0 ALIGN=TOP ALT="" SRC="http://ej.iop.org/images/0305-4470/30/6/004/Full/img81.gif">, iff <i>V</i> = 0;
<P>
(4) <IMG BORDER=0 ALIGN=TOP ALT="" SRC="http://ej.iop.org/images/0305-4470/30/6/004/Full/img82.gif">, iff <IMG BORDER=0 ALIGN=TOP ALT="" SRC="http://ej.iop.org/images/0305-4470/30/6/004/Full/img83.gif"> where <i>C</i> is an
arbitrary constant.
<P>
The above operators have representation (10) with
<IMG BORDER=0 ALIGN=TOP ALT="" SRC="http://ej.iop.org/images/0305-4470/30/6/004/Full/img84.gif">.
<P>
Note that symmetry classification of potentials for the
fourth-order PDE of the form
<P><IMG BORDER=0 ALIGN=TOP ALT="" SRC="http://ej.iop.org/images/0305-4470/30/6/004/Full/img85.gif"><P>
was carried out in [<A HREF="#Sym">8</A>]. In this case, symmetry operators
have representation (10) with <IMG BORDER=0 ALIGN=TOP ALT="" SRC="http://ej.iop.org/images/0305-4470/30/6/004/Full/img86.gif"> and <i>n</i> = 2.
<P>
(iii) Now, let us consider nonlinear PDEs of type (4)
in (<i>r</i> + 1)-dimensional space:
<P><IMG BORDER=0 ALIGN=TOP ALT="" SRC="http://ej.iop.org/images/0305-4470/30/6/004/Full/img87.gif"><P>
where <IMG BORDER=0 ALIGN=TOP ALT="" SRC="http://ej.iop.org/images/0305-4470/30/6/004/Full/img88.gif"> is complex conjugated function, <i> n </i> is an
arbitrary integer power and <i>F</i> is an arbitrary complex function
of <IMG BORDER=0 ALIGN=TOP ALT="" SRC="http://ej.iop.org/images/0305-4470/30/6/004/Full/img89.gif">
<P>
We study symmetry classification of (11), i.e. we find
all functions <IMG BORDER=0 ALIGN=TOP ALT="" SRC="http://ej.iop.org/images/0305-4470/30/6/004/Full/img90.gif"> which admit an extension of
symmetry of equation (11).
<P>
<i> Theorem 4</i>
Equation (11) is invariant under the following algebras:
<P>
(1) <IMG BORDER=0 ALIGN=TOP ALT="" SRC="http://ej.iop.org/images/0305-4470/30/6/004/Full/img91.gif">, iff <i>F</i> is an
arbitrary differentiable function;
<P>
(2) <IMG BORDER=0 ALIGN=TOP ALT="" SRC="http://ej.iop.org/images/0305-4470/30/6/004/Full/img92.gif">, iff <IMG BORDER=0 ALIGN=TOP ALT="" SRC="http://ej.iop.org/images/0305-4470/30/6/004/Full/img93.gif">;
<P>
(3) <IMG BORDER=0 ALIGN=TOP ALT="" SRC="http://ej.iop.org/images/0305-4470/30/6/004/Full/img94.gif">, iff
<IMG BORDER=0 ALIGN=TOP ALT="" SRC="http://ej.iop.org/images/0305-4470/30/6/004/Full/img95.gif">, <IMG BORDER=0 ALIGN=TOP ALT="" SRC="http://ej.iop.org/images/0305-4470/30/6/004/Full/img96.gif">;
<P>
(4) <IMG BORDER=0 ALIGN=TOP ALT="" SRC="http://ej.iop.org/images/0305-4470/30/6/004/Full/img97.gif">, iff <IMG BORDER=0 ALIGN=TOP ALT="" SRC="http://ej.iop.org/images/0305-4470/30/6/004/Full/img98.gif">;
<P>
(5) <IMG BORDER=0 ALIGN=TOP ALT="" SRC="http://ej.iop.org/images/0305-4470/30/6/004/Full/img99.gif">, iff <i>F</i> = 0.
<P>
Here, indices <i>a</i>,<i>b</i> are from 1 to <i>r</i>, <IMG BORDER=0 ALIGN=TOP ALT="" SRC="http://ej.iop.org/images/0305-4470/30/6/004/Full/img100.gif">, <i>k</i> is an
arbitrary number <IMG BORDER=0 ALIGN=TOP ALT="" SRC="http://ej.iop.org/images/0305-4470/30/6/004/Full/img101.gif">, and the above operators have the
following representation:
<P><IMG BORDER=0 ALIGN=TOP ALT="" SRC="http://ej.iop.org/images/0305-4470/30/6/004/Full/img102.gif"><P>