The new boots are lighter and softer, and therefore more comfortable to wear.

We were unable to get funding and therefore had to abandon the project.

以上两句都是 and 连接的并列句，前后是两个并列分句，第二分句省略了主语。

我认为，判断 and 是否连接并列句的标准，符合下面任意一个，则是并列句：

1. 两个分句各有自己的主语和谓语。

2. 第二分句可以省略与第一分句相同的主语。

以下情况除外：

如果 and 连接的是两个其他的成分，如表语 are lighter and softer，则不是并列句。