I'd say "it depends". I usually have a feel for whether or not this seems "likely" that sources will emerge, and if so, generally I'll add what I'd call a "placeholder profile" if there's a good reason to do so. But I do like to have the LNAB first, as I'd much prefer to get it set up correctly the first time, and not have to keep changing the LNAB possibly even multiple times until I get it right. But I will source where I got the information from, so that if I'm asked later, I can at least say "at this poorly sourced spot", so that others can offer suggestions.
But if there's almost no sources, and the sources are unclear, or there's controversy about the LNAB or family, or the information is garbled, I won't create one of those at all. I like to have at least a warm/fuzzy with the data prior to profile creation or else it just means I need to research some more.