I don't feel like there is a long spread that is ever too much. Maybe the incorrect spread is used, or people are not sure how to apply them to the situation. Then it may be harder to follow along. But most of the time, you don't need a deck long spread. You just need to find the right spread that works for you, your intuition and which will actually help you fully evaluate the query.
But I think some readings would really benefit from a larger setup if it is being approached from a grander scale, or what I call "life work" in readings. For example, If I am reading someone's soul, a larger spread would be required if I were to use Tarot to pinpoint each aspect, to identify human body and not, connections, etc. But it depends on the scenario is and what information I am trying to gather. I typically use bigger spreads in general.
Overall I look at tarot card spreads and their slots as 'points of interest' or 'energies' being activated or present in the situation surrounding the query. If you know what influences the query or what needs to be identified to address the nature of it, the spread(s) that need to be used then become more obvious to fix on these energies and pinpoint the dynamics. More like an investigation of sorts with the assistance of your intuition.
Smaller spreads are easier to doubt I think because it forces you to rely more on your intuition and your gut, and not actually confirming 'what is'. For people who question intuition more or are still developing, it could mean not giving themselves enough room to develop the situation into the cards and then having to take leaps of faith in their logic. Mixing it up would be a good idea at this point to find what is comfortable for that person, or just write it down the cards of a longer reading and save them for later in a notebook or through computer. But when I just need to step back and find the message being delivered, a 3 card is more direct, is more succinct and to the point. I don't want a whole lot of 'blah blah blah', I just need to put a focus or take a small sample of the energy to 'get it'.
Depending on the application, any spread can be very powerful. If you are developed enough with your intuition, then you can make use of most spreads with ease. These are just my experiences...