Many people complain of frequent dropped connections and slow performance, not to mention the hit your phone battery takes even when it's getting a bit of a charge from your laptop.
Beyond the technical considerations, however, there's also the issue of your carrier and data plan. If you don't have an unlimited data plan, or at least a generous serving of monthly data, you can go way over your bandwidth limits pretty quickly.
You can offset this a little bit in Windows 8.1 by setting your tether as a metered connection, as well as turning off any sync apps like Dropbox and OneDrive. If you end up using your tethered connection a bunch, consider a proper mobile hotspot like a MiFi or a laptop card instead.
Just pay up
Finally, if I can't get free Wi-Fi and tethering won't work, then it's time to look at paying for Wi-Fi. Sorry to break it to you.
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