#1 By forming a tag team, Bryan vs. Miz can potentially continue around titles

The first thing that comes to mind when a new team forms is the potential of that duo. Any team with Daniel Bryan has immediate legitimacy. When he teamed with Kane, it worked well because not only were both men great at the nuances of the game but the big guy/small guy dynamic made the pairing legitimate. Everything that followed the formation was fruitful and entertaining. The same thing happened when Rowan teamed with Bryan last year. The duo eventually won the vacant SmackDown Tag Team titles.
Once John Morrison came back to the WWE late last year, it didn't take long to figure out his direction. His first appearance was as The Miz's friend. The two then joined the ranks of the SmackDown Tag Team division before quickly capturing the titles from the New Day at Super Showdown.
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After retaining their titles in a hotly-contested match inside the Elimination Chamber, the duo of Miz and Morrison will need new challengers. They'll likely face the Usos and/or the New Day at WrestleMania. The Champs should retain their titles and move on to different challengers. If Gulak and Bryan officially form a team, then they make logical sense as foes for the heel Champs.
The Miz and Daniel Bryan are destined to fight forever in one feud or another. It harkens back to Bryan's debut when NXT was a game show and Miz was his "pro." Battling over the SmackDown Tag Team titles allows their neverending feud to add a new layer.