The problem is that because of how long turn based combat takes its very tedious to have filler combat against weak enemies. So turn based games tend to make most encounters major.
That isn't how it is supposed to work. I don't think this general philosophy has shifted much over time, but the 3.5e Dungeon Master's Guide states:
DIFFICULTY
Sometimes, the PCs encounter something that’s a pushover for
them. At other times, an encounter is too difficult, and they have
to run away. A well-constructed adventure has a variety of encounters
at several different levels of difficulty. Table 3–2: Encounter
Difficulty shows (in percentage terms) how many encounters of a
certain difficulty an adventure should have.
Easy: The PCs win handily with little threat to themselves. The
Encounter Level for the encounter is lower than the party level.
The group should be able to handle an almost limitless number of
these encounters.
Easy if Handled Properly: There’s a trick to this kind of encounter—
a trick the PCs must discover to have a good chance of victory.
Find and eliminate the evil cleric with greater invisibility first
so she stops bolstering the undead, and everything else about the
encounter becomes much easier. If not handled properly, this
kind of encounter becomes challenging or even very difficult.
Challenging: Most encounters seriously threaten at least one
member of the group in some way. These are challenging encounters,
about equal in Encounter Level to the party level. The average
adventuring group should be able to handle four challenging encounters
before they run low on spells, hit points, and other resources.
If an encounter doesn’t cost the PCs some significant portion
of their resources, it’s not challenging.
Very Difficult: One PC might very well die. The Encounter Level
is higher than the party level. This sort of encounter may be more
dangerous than an overpowering one, because it’s not immediately
obvious to the players that the PCs should flee.
Overpowering: The PCs should run. If they don’t, they will
almost certainly lose. The Encounter Level is five or more levels
higher than the party level.
Table 3–2: Encounter Difficulty
% of Total Encounter Description
10% Easy EL lower than party level
20% Easy if handled properly Special (see below)
50% Challenging EL equals that of party
15% Very difficult EL 1–4 higher than party level
5% Overpowering EL 5+ higher than party level
