Big ships are slightly easier to hit, both by the player and even for the AI. (at least for certain versions of Oolite)
There are a few missions/campaigns that are easier if you take a fast Asp instead of a Boa 2.
Trying to do them in an Anaconda, Boa 1, or Python is likely just painful...
But the Asp's money-making abilities are just awful, due to not having any cargo space and rather limited Gold/Platinum capacity. (499 kg of each)
...So only someone already rich can attempt to use it much.
This is where storing ships comes in so handy -- so you can wear whatever "hat" you need for the current task.
And that needs to be even more expensive -- storage fees and/or requiring the ownership of rock hermits/other stations.
This can put a crimp on the range of an explorer if they have only 1 place to switch back into their other ship/s.
Having your "spare" ships transported to you can be game-balanced by multi-day long delays and exorbitant fees (1000+ credits to cross a Galactic Chart, 10000+ to cross to the next Galactic Chart, etc) -- any mission and contract deadlines will likely be blown, which makes even these credit amounts seem tiny.
And then after you get your "spare" ship, your previous one also has to be transported and stored -- More credits gone!
On top of that, both ships will need repairs from travel which is often a few percent of their total value.
There could even be a very low chance of the ships being damaged/destroyed in transport or if their storage facility is attacked.
Pity the poor sod whose ships were stored at a system that went nova...
Being rich-and-powerful shouldn't be cheap.