Do you mean prick out seedlings into them to grow on? Yes, as long as you pierce holes in the bottom so that they can drain.

I found that they are less expensive than the commercial small pots. I use the colored ones just in case the roots don't like exposure to strong light. Then I stick a thick nail in my soldering gun and burn several holes in the bottom of each cup.

I save yoggurt pots to transplant seedling into, but I initially SOW the seed in trays - rather depends on how many seeds you;re sowing I suppose....might be room to sow 4 or 5 seeds in a yogurt pot, but you could sow loads into a single tray (depends on the specific plant you're trying to grow of course). If you want to save money, get along to Pound Stretcher, where you can buy decent seed trays very cheaply. :-)

Always important to have drainage holes in teh bottom, whatever you end up using.

i cant speak for other garden centres but id imagine they have the same excesses . my garden centre let you have all the plastic plant pot holder trays for nothing .i think they mite make good things with a fewholes to bring on seedlings.they have all sorts of sizes to and im sure would have lots of uses as well as this.i like the nail in the soldering iron top tip wilie very good.take care bye for now.