# Math mode: Why \left and \right is considered bad? [duplicate]

A most respected moderator repeatedly advises against the automation of \left and \right in math mode. (Among others, here is one.) There must be some good argument behind that. I am just curious, why?

• For one thing, \left...\right cannot break across lines, whereas \big etc. have no such limitations. I would guess the other argument is that one should deliberately choose their delimiter sizes, rather than trusting them to an algorithm. – Steven B. Segletes Aug 14 '17 at 13:59
• Try $a(b+c)$ and $a\left(b+c\right)$ – egreg Aug 14 '17 at 14:00
• Often scaled to be too high. Excessive use (where there are no scaling being done) makes the math code a lot harder to read. – daleif Aug 14 '17 at 14:01
• see for example tex.stackexchange.com/a/173740/1090 (I suspect this question is a duplicate of that) – David Carlisle Aug 14 '17 at 14:05
• adding new questions on to existing ones doesn't really work (especially after the question has been closed, but even if not) the site works best with one question per post. (but yes stay away from commath:-) – David Carlisle Aug 14 '17 at 15:37