Don’t abuse the feature, as always. If they are not absolutely necessary, don’t use them. Whatever you add to your main text (tables, frames – including images --, sections, drawing objects, …) has an impact on the document structure. Keep it as simple as possible for reliability and stability. Note also that direct formatting puts a considerable stress on Writer; you might not notice it on small documents but it becomes more and more perceptible as the document grows. Consequently, styles are mandatory for non-expendable documents. And by styles, I mean all of them: paragraph, character, page, frame and list. Character styles are frequently neglected (because they don’t exist in M$ Word) but they are a key in formatting success. List styles are also disregarded (for the same reason) because an emulation of Word workflow is provided but this is a sin against reason (the feature in Word is a real mess and this mess is forwarded to Writer – unless you switch to list styles). I kept frame styles for the end: their concept is difficult to understand and mastering their configuration is super-expert skill. However they ensure predictability and stability in positioning your frames and images which can’t be achieved otherwise (which would end up in direct formatting).
I did not mention “table styles” because they are not styles but behave like a collection of macros which are fired under various circumstances (when you expect the least). If you’re satisfied with the layout and look designed by the “style” author, that’s fine. However, if you intend to customise your tables, stay far away from these table “styles” because “macro triggering” will erase/mask your customisations and add its layer of direct formatting.