Under what conditions does a Martial Spellcaster need the Warcaster feat to comfortably cast spells?

I had a player recently come to me about playing an Eldritch Knight character, and they had questions about their ability to cast spells while holding a weapon (or two), and were debating taking the Warcaster feat (PHB, 170) to mitigate specifically those issues. At my table, I try to take the somatic/material component requirements of spells seriously, so I want to make sure I have a grasp of what can or cannot be done when a spellcaster holding weapons tries to cast a spell, or return to attacking after having cast a spell.

One thing I’m especially interested in is the degree to which the character can "comfortably" do the actions listed. "Comfortably" in this context means that the character isn’t taking certain actions which might be technically legal according to the rules of the game, but which might inconvenience them under common circumstances. A common example is a Two Weapon Fighting character who drops a weapon to the ground to grab their spellcasting focus for casting; if they have to move, they risk leaving their weapon behind on the ground, so from my perspective, this wouldn’t qualify as a "comfortable" maneuver.

So, for the following builds, under what conditions is the character able to cast spells, and to what degree does the Warcaster feat improve their ability to do so?

  • Holding a one-handed weapon
  • Holding two one-handed weapons
  • Holding a one-handed weapon and Shield (neither Cleric nor Paladin)
  • Holding a one-handed weapon and Shield (Cleric or Paladin)
    • I’m separating these two out because Clerics and Paladins both get the ability to affix a Holy Symbol to their shield and therefore use their Shield as they would a Material Component. So I think the answer to this question is necessarily different depending on whether the spellcaster is a paladin or an Eldritch Knight, for example.
  • Holding a two-handed weapon