Tabletop Gaming

Some of the chronic problems for 5E mitigated by pacing:

• Short rest / long rest balance. Classes which recharge spells or abilities on a long rest rather than a short rest tend to be noticeably stronger. But if you add just a little time pressure, you'll notice your players take fewer long rests and more short rests, kind of "soft correcting" the problem.
• Martial / caster divide. Time pressure cannot fix this balance issue, but it helps. Martial characters usually do not need to stop as often as casters, so their ability to press on when others are exhausted becomes valuable again.
• Spell duration and ritual casting. Without time pressure, there's no reason to not use ritual casting, and a 10-minute spell is usually inferior to a 1-minute spell. But if your players are moving through a dungeon at a steady clip, that 10-minute spell now easily covers two encounters instead of one, and the group may not want to stop for the ritual casting of a spell.
• The "pile-on" phenomenon. If one player with +6 to athletics tries to lift a DC18 trapdoor, there's a 45% chance of success. But there's nothing in 5E saying a party of 5 adventurers can't just take turns trying the same check. 5x adventurers with +0 to athletics have a 55.63% chance of opening that same trap door. Even worse, there's nothing saying one persistent adventurer can't just repeatedly try an ability check until they succeed. Now, the wizard with -1 strength has a 100% chance to open the trap door (eventually). This trivializes ability checks. Trying to arbitrate why players can't try more than once is possible, but taxing. But if instead you just give them a little time pressure, the players tend to spend their limited time doing things that are more likely to succeed first try, and they're definitely not going to sit around and wait for the guy with -1 strength to beat the strength puzzle.
• The "point-and-click-adventure" problem. Sometimes, players get a little tunnel-vision while trying to solve an obstacle, and they do that thing where they try every object in their inventory like it's Monkey Island. 5E is particularly vulnerable to this because the crunchy ruleset makes players think there's a "right" answer to a problem (with published books, that's often true), but the unstructured nature of the adventures make it unclear what that answer is. This murders dramatic tension and narrative momentum. But with a little time pressure, players will respond to time-consuming distractions by saying, "Gee, there's got to be a better way," and they'll inevitably gravitate towards more intuitive solutions that make sense in the context of the adventure.

I am addicted to bullet points, lol.

There are other chronic problems with 5E that aren't solved by good pacing -- the social and exploration pillars are bizarrely underdeveloped with no gameplay loops and this leaves combat with an over-emphasized role, wilderness survival and overworld travel are such a chore that everybody skips them, stealth mechanics are self-contradictory, crafting explicitly boils down to "the DM makes something up," some magic items are ridiculously powerful/useless for their rarity, the random loot drops are extremely random, the random encounters in the published adventure books are almost exclusively deathmatches, they never should have gotten rid of "out of combat turns," the list goes on.

I would generally categorize these as balance problems (balance between pillars of adventuring is a kind of balance). And I'll repeat that you shouldn't trouble yourself with solving them. If you're used to 3.5, then all you really need to do is follow your instincts for how a D&D session should feel, and don't think to hard about anything I just told you.