I do both and have noticed, altho I haven't been doing many nails since lockdowns, more clients are opting for this, so they don't have to bother about Shellac removal. I have a lot of clients in healthcare too, so as the others said, they sometimes find polish easier.
I don't carry a huge stock of colours, but I do let my clients know this, and ask them to let me know in advance if they have a particular colour in mind, so I can make sure I have it for them. I definitely have more Shellac colours in stock.
As someone has said, clients often do toes in polish, so opt for a good trade brand who does both, so for example, I use CND and can get Shellac for their fingers and put the same colour on their toes in Vinylux.
Also, if doing polish ...take payment at start....tell them to keep jacket on, car keys out, etc. These are the usual ways they touch polish on the way home! If ur mobile, it should be easier.