I trade a lot of calendars. I will often just open with a 1 lot position to get an idea of what is a realistic price to pay if the spread is wide. Eg, if the spread is quoted at 1.20 - 2.00, I will see if my 1 lot trade fills at 1.5, and if not, then I will gradually increase it until it fills. Then I will pile in with my full allocation.
I do the same on closing.
On some high price stocks like BKNG, where a simple long call can cost 80 ($8,000) per lot, it's understandable to see why most orders are for very small sizes like 1-2 lots.