I think Trail of Cthulhu, and other GUMSHOE games as for as I've seen, have the mecanic of spending resources during the investigation for various reasons. The first is that it makes sure that no single player can steal the spotlight from the rest of the players since they are limited in what resources and skills they can use and how many times they can use it.
It also means that the strategies that the investigators take need to keep varying. For example, they will not always be able to talk their way out of everything- sometimes they will be forced to hide, use their contacts, fight, or run away.
The resource management is also a nod to horror games where you need to think ahead in regards to how many resourcfes you are willing to spend now, knowing that it might mean that in the future you will not have that resource to spend.
For one part, I like the GUMSHOE system in that it always makes sure that the PCs get the main clues, though then they need to spend skill points to analyze the clues. However, I much prefer to go the Masks of Nyarlathotep route in that it adds an overabundance of clues and makes the character roll for them to find them: as a player there is less of a sense of being railroaded since there is still a chance to succeed or fail in the clue-gathering aspect, and as a GM you know that players are still receiving a bunch of clues that will eventually lead the players in the same direction.
I also like to reuse clues- if the players for some reason or another manage to botch all their rolls to find a clue, I'll put the clue in another scene so they get another chance to find it. That way, if they miss an important clue they will eventually find it even if it is later in the investigation.
I'd reccomend reading this essay:
http://www.thealexandrian.net/creations/misc/three-clue-rule.html Very informative and has great tips for GMs.