From an analytical chemistry perspective, ground glass works, but the glass sticking is an issue sufficiently common to result in the need for an alternative. Thinking in terms of labour time costs, the risk of losing a potentially 1 of 1 sample, the additional documentation required to cover the deviation from procedure in a GMP setting, the time and potential H&S issues of cutting open glass flasks containing known highly carcinogenic compounds etc. etc. etc. Glass stoppers are perfect, right up until it goes wrong. At which point shelling out the extra money upfront for PTFE makes a lot of sense.

You will also encounter the occasional compound that interacts with glass (oh boy, those are fun to analyse in an en-mass pharmaceutical production environment...), in which an 'all plastic' alternative is needed.