For example, you may certainly contact your host at any time, but when are they available to respond to your questions and concerns? How long will it take for someone to get back to you? Will there be someone to help you if your mission-critical website goes down at 3:00 in the morning? What language(s) do your host providers speak? Support in Malagasy is probably essential if you live and work in Madagascar, but fairly useless if you are in North America.
In terms of what many vendors call unlimited service, Web Hosting Pad's terms of service indicate that their definition of unlimited is what they call "incremental." Basically, as you need more capability, they want to discuss that with you, both to help you get the most out of their services, and to make sure you're using their systems without abusing them.
Many services offer a low "starting price," but require you to prepay for two or three years of service to get that price. After the promotional period, the renewal price for some services can be two, three, or even four times the initial promotional pricing. While the initial deal might be incredible, the cost of transferring your site (or paying the added fee) in a couple of years may be something to consider.