Weapon swap

To weapon swap refers broadly to the action of changing your current weapon set, usually by pressing F1 to F4. This has a range of applications.

Enchanting
One basic application is to keep your normal weapon set on one swap, and keep another weapon with an of Enchanting upgrade, and switch to the Enchanting weapon when it is time to cast a long lasting enchantment such as Elemental Attunement or skills that benefit largely from even an extra second such as Aegis or enchantment-based speed boosts.

Energy
Swapping up or swapping down to hide energy is a necessary skill in mitigating energy denial. If you are likely to be the target of energy denial, keep a weapon with a Brawn over Brains inscription and a shield. Instead of using a shield there is a quest reward from the quest Cities of Ascalon which can give you -2 energy when you don't meet the requirement for it. This makes you able to hide even more energy. The weapon set with a shield, which is the most common choice, will grant a total of -5 energy while equipped, and if your primary set has +10, +12, +15, or +17, you are able to hide up to 22 energy by switching to the low energy set. Energy that is hidden in this way cannot be destroyed by foes using skills like Energy Burn or Debilitating Shot or by using skills like Purge Signet. This can also be used to prematurely end hexes with an 'ends if target foe's energy reaches zero' clause such as Malaise.

Offense
Another highly useful application is having an offense swap to be used for casting anything. A good example would be a Fire Magic Elementalist using a Fire Magic Wand with a Wrapping of Memory, and an Aptitude not Attitude Inscription, and a Fire Magic Focus with a Focus Core of Aptitude and a Forget Me Not inscription for a combined double 20% chance to both cast Fire Magic skills faster, and have them recharge faster. This is usually referred to as a '40/40 swap'.

Defense
Players often commonly use a defensive swap to be used while under attack. To complement an offensive swap, a one handed Martial weapon with an "of Defense" (or "of Fortitude") upgrade and a shield with an "of Fortitude" upgrade grants an additional 30 health and 13 AL (or 60 health and 8 AL), even if you do not meet the requirement of the shield. +13 AL sets are a better choice for reducing damage, while a +60 health set is more useful in surviving in situations that have already pushed the player to low health, such as during spikes or while under health degeneration. The shield can also be further inscribed for extra defense against certain damage types, like Piercing or Lightning. It is not uncommon for players to carry shields inscribed against each type of damage in their inventory and to switch the equipped shield depending on what type of damage they are taking. Alternatively, a simple "reduces physical damage" mod can be used on shields for more general-purpose defense.

Faster resurrection
Using a Wand and Focus each with a 20% chance of halved cast time can improve the cast time of spells like Resurrection Chant or Flesh of My Flesh, even if you do not meet the requirements in Healing Prayers or Restoration Magic.