Vegetable butter, as the name suggests, is not really butter. It is a substitute for butter made by partially hydrogenating vegetable oil and adding artificial flavors to mimic the taste of butter, and can be used in place of butter on general occasions. And, because it is artificial, it has a very flexible melting point. The melting point varies greatly from one margarine to another.
Let's review the melting point of butter first. It's about 34 degrees, very soft at 28 degrees, and very hard when refrigerated at 0-4 degrees. But vegetable butter is considerably different. Depending on the variety, some remain soft even when refrigerated, which makes it suitable for spreading bread; some remain very hard even at 28 degrees, which makes it suitable for breading, and much easier to work with than butter for making lasagna.
If you're asking: With all the benefits of margarine, can it be used as a substitute for butter? Theoretically maybe, but practically it's impossible - and that may be the gap between ideal and reality.
The first weakness of vegetable butter is its poor flavor and texture. How can artificial flavors match the natural flavor of butter? Moreover, its texture makes people feel uncomfortable when they eat it. Therefore, bakers still insist on using butter if they want to make high grade pastry. The second weakness of vegetable butter is even more deadly, vegetable oil after hydrogenation, will produce trans fatty acids, early people do not know enough about trans fatty acids, so vegetable butter is more widely used. But with the depth of research now, the harm of trans fatty acids is increasingly recognized, especially on the cardiovascular harm is great. Therefore, it is better not to use vegetable butter if you can.
By the way, the kind of vegetable butter that is still soft in the refrigerated state can not be used to make lasagna pastry, otherwise, it will be leaking oil leakage in a mess.