Generally in a competitive market, like we have seen in the GTA over the past many years, it can typically take several months and many bidding wars to finally secure the property of your choice. For that reason, buyers would buy a home first and then list their current one for sale after. This was typically a safe bet and did not cause any concern in a hot market. There was also the consideration that many families took which was to live with friends of family or rent a space in the event there was a gap between the two closings.
However today, I would raise caution to ensure that if you were to buy a home first and sell your current one after, that you fully understand the risks associated. If a listed home is not garnering a healthy amount of showings or offers then it is natural for a seller to feel pressured to reduce the price as they likely do not have the luxury of time to wait it out. I came across this situation just last week (call me if you want to know all the details!). Lowering the price could be a great opportunity to allow for a fresh buyer pool, but it would have to be within reason and ultimately affordable for the sellers. In most situations a seller has a benchmark price they need to meet in order to afford the home they have newly purchased, so there is a limit here to adjusting the listing price.