Silver foil is better for inclusions than silver leaf as there is more substance and so less likelihood that it will burn away.
Sterling silver – not that common in foils – will darken easily on exposure to temperature and air.
Silver foil will also react with some glass colours. A good guide to this can be obtained from Bullseye’s chart on glass interactions. This shows which glasses react with silver. To minimize the reactions, minimize the amount of time spent above 600C.
Only a short bubble squeeze is required with foil as it is not so stiff that it will resist the weight of the glass on top, so creating bubbles. A short squeeze to allow the air out is still a good idea.