The only hostel we've stayed in where we had to rent linens was in Sweden, and it cost a fortune! Would have been cheaper to buy our own. But lots of hostels don't require them. On another trip, I used mine a lot on trains and overnighting at stations for an extra layer of warmth. It's amazing the difference a thin piece of cotton makes. For your purposes, I'd suggest looking at the rates at the hostels you want to stay at, or at half a dozen in the cities you're visiting. If most or all of them provide free linens, it's probably not worth taking. If not, throw it in. They're not very big or heavy, especially if you splurge on the silk ones.